Loans Loans, Loans by Credit Quality Indicator (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 20,931,460	$ 20,054,716
Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	20,279,634	19,251,353
Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	182,400	176,918
Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	258,909	351,142
Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	210,517	275,303
Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans	6,534,660	6,489,014
Commercial and industrial | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	6,101,491	5,937,119
Commercial and industrial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	157,106	141,328
Commercial and industrial | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	153,779	227,196
Commercial and industrial | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	122,284	183,371
Commercial real estate — owner occupied
Financing Receivable, Recorded Investment [Line Items]
Loans	827,064	897,724
Commercial real estate — owner occupied | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	742,257	805,871
Commercial real estate — owner occupied | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	11,741	17,785
Commercial real estate — owner occupied | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	57,468	64,524
Commercial real estate — owner occupied | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	15,598	9,544
Commercial and business lending
Financing Receivable, Recorded Investment [Line Items]
Loans	7,361,724	7,386,738
Commercial and business lending | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	6,843,748	6,742,990
Commercial and business lending | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	168,847	159,113
Commercial and business lending | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	211,247	291,720
Commercial and business lending | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	137,882	192,915
Commercial real estate — investor
Financing Receivable, Recorded Investment [Line Items]
Loans	3,345,536	3,574,732
Commercial real estate — investor | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	3,284,497	3,491,217
Commercial real estate — investor | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	10,726	14,236
Commercial real estate — investor | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	46,770	51,228
Commercial real estate — investor | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	3,543	18,051
Real estate construction
Financing Receivable, Recorded Investment [Line Items]
Loans	1,552,135	1,432,497
Real estate construction | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	1,550,462	1,429,083
Real estate construction | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	15	105
Real estate construction | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	118	2,465
Real estate construction | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	1,540	844
Commercial real estate lending
Financing Receivable, Recorded Investment [Line Items]
Loans	4,897,671	5,007,229
Commercial real estate lending | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	4,834,959	4,920,300
Commercial real estate lending | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	10,741	14,341
Commercial real estate lending | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	46,888	53,693
Commercial real estate lending | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	5,083	18,895
Total commercial
Financing Receivable, Recorded Investment [Line Items]
Loans	12,259,395	12,393,967
Total commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	11,678,707	11,663,290
Total commercial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	179,588	173,454
Total commercial | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	258,135	345,413
Total commercial | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	142,965	211,810
Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Loans	7,408,471	6,332,327
Residential mortgage | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	7,352,286	6,275,162
Residential mortgage | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	881	1,314
Residential mortgage | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	650	5,615
Residential mortgage | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	54,654	50,236
Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans	890,130	934,443
Home equity | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	876,003	919,740
Home equity | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	1,364	1,588
Home equity | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	124	114
Home equity | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	12,639	13,001
Other consumer
Financing Receivable, Recorded Investment [Line Items]
Loans	373,464	393,979
Other consumer | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	372,638	393,161
Other consumer | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	567	562
Other consumer | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Other consumer | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	259	256
Total consumer
Financing Receivable, Recorded Investment [Line Items]
Loans	8,672,065	7,660,749
Total consumer | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans	8,600,927	7,588,063
Total consumer | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans	2,812	3,464
Total consumer | Potential Problem
Financing Receivable, Recorded Investment [Line Items]
Loans	774	5,729
Total consumer | Nonaccrual
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 67,552	$ 63,493